The most common and most likely answer to this crossword clue is the 4 plus 6 plus 2 plus 4 letter word PILE PELION ON OSSA
I've seen this crossword clue in The Guardian
P
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L
E
P
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N
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S
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A
Buddy explains!
The straight part
We know that "make things worse" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case make things worse = pile pelion on ossa.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.